A variety of diepoxy compounds each having two cycloaliphatic skeletons per molecule are currently commercially available as, for example, CEL-2021 (3,4-epoxycyclohexylmethyl 3′,4′-epoxycyclohexanecarboxylate), CEL-3000 (1,2,8,9-diepoxylimonene), and CEL-2081 (a ∈-caprolactone oligomer combined with 3,4-epoxycyclohexylmethanol and 3,4-epoxycyclohexanecarboxylic acid at both ends through ester bond, respectively), each of which is available from Daicel Chemical Industries, Ltd. CEL-3000 contains methyl group in carbon constituting epoxy group and thereby has a lower reactivity of epoxy group than compounds which do not contain such methyl group. CEL-2021P and CEL-2081 are hydrolyzable, because they have ester bond in the molecule. Accordingly, cured products of them may have impaired properties when used at high temperatures and high humidity or used under such a condition that a strong acid is formed. Demands have therefore been made to provide epoxy compounds having a cycloaliphatic skeleton with no ester bond in the molecule.
Japanese Unexamined Patent Application Publication (JP-A) No. 48-29899 discloses a cured article of a cycloaliphatic diepoxy compound obtained by synthetically preparing a diepoxy compound represented by following compound (II):
wherein X is CH2; and R1 to R18 are each hydrogen atom, and carrying out a curing reaction of this compound with an acid anhydride. The document mentions that the resulting cured article has improved properties as compared with cured articles of known cycloaliphatic diepoxy compounds. This technique, however, uses perbenzoic acid for the preparation of the cycloaliphatic diepoxy compound and is hard to use industrially. Japanese Unexamined Patent Application Publication (JP-A) No. 58-172387 discloses a technique of synthetically preparing a percarboxylic acid from hydrogen peroxide, an acid catalyst, and an organic acid, extracting the percarboxylic acid with an organic solvent, and carrying out epoxidation of the extracted compound. This technique employs long procedures, yields large amounts of waste materials, and requires complicated operations. In addition, the percarboxylic acid contains not only water but also hydrogen peroxide and the acid catalyst, even though in trace amounts, and may thereby become unstable and be reduced in concentration in a short time in the reaction step for the preparation of the percarboxylic acid and extraction step. The reduction in concentration of the percarboxylic acid also causes oxygen formation, and formed oxygen makes inside of the reactor dangerous and invites side reactions of the epoxidized product typically in the epoxidation reaction step and a step of purifying the resulting epoxy compound. Such by-products reduce the recovery of the target product and contaminate the preparation apparatus. Thus, the technique is industrially disadvantageous.
Japanese Unexamined Patent Application Publication (JP-A) No. 2002-275169 discloses a technique of synthetically preparing a cycloaliphatic diepoxy compound represented by General Formula (II) by oxidizing acetaldehyde with air to yield peracetic acid, and epoxidizing a compound having two cycloaliphatic olefin skeletons and containing no ester bond in the molecule with the peracetic acid. However, only desolvation is conduced in the synthetic preparation of the cycloaliphatic diepoxy compound, and the product contains high-molecular weight components having shorter elution times than that of the cycloaliphatic diepoxy compound detected in gel permeation chromatography (hereinafter referred to as “GPC”) analysis; impurities having shorter retention times than that of the cycloaliphatic diepoxy compound represented by General Formula (II), as well as reaction intermediates, as detected in analysis using a gas chromatograph (hereinafter referred to as “GC”). The product is insufficient in color (APHA) and insufficient for use in display materials, such as liquid crystals, requiring thermal stability and/or optical transparency.
Patent Document 1: Japanese Unexamined Patent Application Publication (JP-A) No. 48-29899
Patent Document 2: Japanese Unexamined Patent Application Publication (JP-A) No. 58-172387
Patent Document 3: Japanese Unexamined Patent Application Publication (JP-A) No. 2002-275169